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2016-12-23sndcp: Allow empty SNDCP-XID indicationsPhilipp1-6/+8
In some rare cases the modem might send a xid indication that does not contain anything except the version number field. The sgsn ignors such SNDCP-XID indications by stripping the entire field from the response. We found a modem in the wild that started to act problematic when the empty SNDCP-XID was missing in the response. This patch changes the XID negotiation behaviour in a way that if a modem should send empty SNDCP-XID indications, the reply will also contain an empty SNDCP-XID indication. Apart from that the SNDCP-XID version number is now parsed and echoed in the response. This ensures that we always reply with the version number that the modem expects. (The version was 0 in all cases we observed so far) Change-Id: I097a770cb4907418f53e620a051ebb8cd110c5f2 Related: OS#1794
2016-09-24SNDCP: add SNDCP-XID encoder/decoder and unit testPhilipp1-0/+216
The SNDCP-XID (or layer-3 xid) is used to exchange layer-3 parameters such as compression. The encoder encodes a bytestream that is then sent as regular XID field from LLC. We will need the SNDCP-XID to negotiate the parameters for our upcomming GPRS data and header compression features Change-Id: If2d63fe2550864cafef3156b1dc0629037c49c1e